Image projection is used in a variety of different applications. For example, electronic slide shows and presentations are frequently projected onto a wall or screen for viewing by a relatively large audience. Additionally, many television and home entertainment systems use an image projected onto a wall or screen to provide a much larger display than is readily available using a monitor or cathode ray tube.
As image data, both still and motion picture, is created and stored digitally, digital projectors have been created that project high quality images onto a viewing surface using digital image data. Examples of digital projectors include digital mirror devices (DMD) and liquid crystal display (LCD) projectors. A DMD uses hundreds of thousands of individually-addressable reflective micro-mirrors to create an image for projection. An LCD projector uses an array of individually driven light absorbing or transmissive LCD panels to create an image for projection.
Both DMD and LCD projectors utilize high intensity lamps and reflectors to generate the light needed for projection. Light generated by the lamp is concentrated as a ‘fireball’ that is located at a focal point of a reflector. Light produced by the fireball is directed by the reflector into a projection assembly that produces images and utilizes the generated light to project the image onto a viewing surface.
In addition to generating the visible light used for projection, projection lamps also naturally produce both infra-red and ultraviolet radiation. This non-visible radiation is undesirable because it heats up the system, is potentially unsafe for the human eye, and can damage some optical components over time. Consequently, projection systems have typically included infra-red and ultraviolet filters to remove such unwanted components of the projection beam.